Magnesium silicon carbide (SiC/Mg) has important applications, for example as mirror coating for solar physics, spectroscopy, plasma physics, photolithography instrumentation and applications related to tabletop extreme ultraviolet (EUV) laser sources. Unfortunately, this Multilayer is extremely prone to degradation exhibited as corrosion spots which randomly and sporadically develop on the SiC/Mg coatings, and are attributed to the corrosion of the Mg layers inside the multilayer after exposure to environmental species such as air and humidity. Thus, the poor aging properties of this multilayer prevent its use in applications which require long-term stability.
SiC/Mg was initially selected and implemented as the reflective coating for NASA's Solar Dynamics Observatory (SDO) solar space mission, to image the solar corona He II and Fe XVI spectral lines at 30.4 and 33.5 nm, respectively. However, due to the poor aging properties of SiC/Mg, corrosion spots developed thus leading to performance degradation. As a result, such characteristic tendencies toward corrosion have prevented SiC/Mg from being widely used.
Alternatively, silicon carbide silicon (SiC/Si) multilayers for 30.4 and 33.5 nm have been used on SDO instead of SiC/Mg. In such cases, however, the use of SiC/Si dramatically decreased the throughput of the 2-mirror telescope camera at 30.4 and 33.5 nm by a factor of 10, due to much lower reflectivity of SiC/Si compared to SiC/Mg.
So far, all prior research and publications devoted to the development of these coatings have been focused on the optical performance (reflective properties) of the coatings, measured on un-corroded regions within the coated area, and do not address the corrosion phenomena. However, this approach is clearly incomplete since the aging properties largely determine the usefulness of these coatings in space and in other applications where good lifetime stability is essential.
Therefore, it would be beneficial to the field of reflective and refractive optics to be able to identify corrosion-resistant multilayer structures along with high peak reflectivity, low stress and high thermal stability in the extreme ultraviolet spectral range that are also capable of avoiding the problems associated with corrodible materials.